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Sugarcane top borer Scirpophaga excerptalis Photo: Erik Karits · Pexels License · source ↗

Sugarcane top borer (Scirpophaga excerptalis)

The sugarcane top borer Scirpophaga excerptalis Walker (formerly Scirpophaga nivella in older Indian literature; also classified as Tryporyza nivella intacta) (Lepidoptera: Crambidae) is the most damaging pest of subtropical Indian sugarcane in Uttar Pradesh, Bihar, Uttarakhand, Punjab and Haryana. Unlike early shoot borer that attacks young shoots, top borer targets the growing point ("spindle") of older canes from 4 months onward, killing the apical bud and producing the characteristic "dead heart of grown cane" symptom and bunchy "shot-hole" leaves.

Identification

  • Adult: silvery-white moth, 12-15 mm long, females with a tuft of orange-brown anal hairs used to cover egg masses; nocturnal
  • Egg: laid in flat creamy masses of 25-65 eggs on the underside of unfurled top leaves, covered with the female's anal hair tuft (orange-brown fluff)
  • Larva: smooth, dirty white to pale yellow, no longitudinal stripes (distinguishes from early shoot borer); full-grown 20-25 mm; head capsule pale brown
  • Damage symptoms (5 generations, each with distinct symptom):
  • First generation (March-April): "dead heart" in young plants, similar to early shoot borer but the bore hole is on the unfurled top whorl
  • Second generation (May-June): characteristic "shot holes" on unfurled top leaves — straight transverse rows of holes that appear when the unfurled leaf opens
  • Third generation (July-August): "bunchy top" — multiple side shoots emerge below the killed growing point, giving a fan-like appearance
  • Fourth and fifth generations (Sept-Nov): kill the top of grown canes, stunt growth and reduce sucrose

Hosts and lifecycle

Highly specific to Saccharum — sugarcane and a few wild grasses. Five overlapping generations from March to November in subtropical India. Egg incubation 5-7 days; larval period 30-40 days; pupation 7-10 days; lifecycle 45-60 days. Larvae enter the unopened leaf whorl, bore down the midrib, and reach the growing point. Pupation occurs inside the bored stem. UPCSR Shahjahanpur and ICAR-IISR Lucknow have characterised this as the no.1 subtropical cane pest by recovery loss.

Damage and economic impact

Top borer is uniquely damaging because the killed growing point cannot be replaced — the cane stops elongating and side shoots (bunchy top) are not millable. AICRP-Sugarcane data records 20-30% cane yield loss and 1-2 percentage point recovery loss in heavily infested UP/Bihar plantings. Co 0238 is moderately susceptible to top borer, which is one reason why even healthy red-rot-free Co 0238 cane in eastern UP runs below 11% recovery in top-borer hotspot years.

Management

ICAR-IISR Lucknow integrated package:

  • Cultural: hand-removal and destruction of egg masses (recognisable by the orange-brown hair tuft) from January to March before larval emergence; removal of "shot-hole" leaves with larvae inside; trash mulching to interfere with adult emergence
  • Resistant varieties: Co 0118, Co 05009, Co 98014, CoLk 94184 show better field tolerance than Co 0238
  • Bud-chip nursery transplanting (see sugarcane-bud-chip-nursery) lets the seedling pass the first vulnerable generation
  • Biological:
  • Egg parasitoid Trichogramma japonicum released at 50,000/ha at 10-day intervals from January through April (8-10 releases) — the recommended primary biocontrol
  • Larval parasitoid Isotima javensis released at 100 mated females/ha at 90 DAP where established
  • Chemical: at egg-mass appearance (Jan-March): chlorantraniliprole 18.5 SC at 375 ml/ha soil drench, or fipronil 0.3 G at 25 kg/ha basal application near plant base. For mid-season generations, drone or knapsack spray of chlorantraniliprole 0.3 ml/L on the whorl
  • Avoid broad-spectrum foliar pyrethroids that decimate Trichogramma populations

See also: Sugarcane crop, Co 0238 sugarcane, Sugarcane early shoot borer, Sugarcane ratoon crop, Sugarcane mealy bug, Sugarcane bud-chip nursery.

Sources

  1. Sugarcane top borer management. ICAR-Indian Institute of Sugarcane Research, Lucknow.
  2. AESA based IPM Sugarcane. National Institute of Plant Health Management.
  3. Sugarcane research bulletins. UP Council of Sugarcane Research, Shahjahanpur.